Vacuum tube keying and control circuit



Dec. 9, 1941. P. D. AND'REWS 2,265,714 1 VACUUM TUBE KEYING AND CONTROL CIRCUIT Filed Aug. 22, 1940 T0 AUX/L/AHY (0N THOL CIRCUITS T0 VOLTAGE sou/ms T0 VOLTAGE SOL/HOE T0 VOL TA GE 5 OUHCE Inventor: Paul D. Andrews, b Jaw a. JM/M His Attorneg.

Patented Dec. 9, 1941 VACUUM TUBE KEYING AND CONTROL CIRCUIT Paul D. Andrews, Schenectady, N. Y., assignor to General Electric New York Company, a corporation of Application August 22, 1940, Serial No. 353,707

(Cl. 178-66) I 8 Claims.

My invention relates to keying and control circuits for radio transmitters and the like, particularly to remote controlled keying circuits for such uses, and its general object is to provide a simplified keying and control system which, however, is highly eflicient and which is capable of meeting severe and unusual constructional and operational requirements.

In one method heretofore proposed and employed for the keying of transmitters a keying tube is connected in series with an amplifier tube of the transmitter. To key the amplifier the value of the impedance introduced in series with the anode-cathode circuit of the amplifier by the keying tube is varied. For this latter purpose a keying device is employed to control the bias voltage of the control electrode of the keying tube relative to its cathode.

Difficulties have been encountered in adapting the above-described keying method to transmitter systems, especially to meet particular conditions. For example, in certain cases the equipment was required to be keyed at extremely high speeds, as at speeds corresponding to 1000 words per minute thereby being capable of adaptation to facsimile use. The keying was required to be accomplished from a remote point, over a twoconductor line, and the key-controlled voltage on this line was preferably limited to volts D. C. The current taken from the two-conductor line was required to be held in a low minimum or to a neglible amount, the keying preferably being accomplished by voltage variation only, in order to permit keying at the desired extremely high speeds. The keying tube connected as a varying impedance in series with the amplifier tube was required to pass a current of 80 to 100 milliamperes with a voltage drop across the keying tube preferably not greater than 50 volts.

Heretofore in transmitters incorporating keying circuits of the type above mentioned in which a keying tube was connected in series with an amplifier tube to be keyed, a triode, such as the type 801A, was generally employed as the keying tube. Assuming an anode to cathode potential of 500 volts, cutoff for this tube occurs at a control electrode voltage of approximately -62 volts. If the voltage of the control electrode be changed by 30 volts in the positive direction anode current causes a voltage drop through the tube of approximately 440 volts. This type of tube therefore fails to meet the required conditions of high anode current and low voltage drop, with limited change of the order of 30 volts only in the control electrode voltage, and negligible or zero current in the keying control line conductors.

Another type of tube which might be considered for use as a keying tube in the manner above described is a tetrode, for example type 865, of approximately the same capacity as the above mentioned triode. At an anode to cathode potential of 500 volts and a screen grid potential of 125 volts, out 01f for this tube occurs at approximately -40 control electrode voltage. If the control electrode voltage be changed 30 volts in thepositive direction, to 10 volts, anode saturation occurs at a current value of approximately 12 milliamperes. If this tube were to be caused to pass a 100 milliampere anode current, with a drop through the tube of 100 volts, it would be necessary to change the control electrode voltage to over +125 volts. Thus this tetrode typetube also fails to meet the required operating conditions above specified.

A still further type of tube which might be considered for use as a keyingtube in the manner described is a pentode, of approximately the same capacity as that of the two types above mentioned. The type 837 would be typical of such a pentode. At an anode to cathode potential of 500 volts, with the screen grid held at +200 volts and the suppressor grid at +40,volts, cutofi occurs at a control electrode voltage of approximately --30 volts. However, if the control electrode voltage be changed by 30 volts in from the cutoff point to bring it to --32 volts,

the voltage drop across anode and cathode is 500 volts and the anode current is only about 40 milliamperes. Even if the control electrode voltage be made zero, a resulting milliampere the positive direction, to its zero control electrode voltage point, the voltage drop across the tube is about 200 'volts' for the desired anode current of 100 milliamperes. Thus although this latter tube passes the required high current, the tube nevertheless would not prove satisfactory in meeting the specified keying conditions since the drop across the tube would be excessive.

I have discovered that difficulties heretofore encountered in employing a keying tube in series with an amplifier or other tube to be keyed are obviated, and in particular that the especially severe keying conditions hereinabove set forth, i. e., high current capacity in the keying tube, low tube drop at this high current, small required range of control electrode bias voltage, and substantially zero current in the line conductor of the remotely controlled keyingcircuit,

v the electrons,

are fully met, by providing in the keying system of the transmitter a keying tube of the beam type, for example, a beam tube of type 807.

The desirable characteristics of the beam tube which make it possible for this tube to meet the requirements of such special operating conditions as above mentioned, and which are not met in a satisfactory manner by other tubes such as the usual triodes, tetrodes, and pentodes, are due,'among other design features, to the fact that in the beam type of tube a means, comprising deflecting plates connected to and at the potential of the cathode, is provided for confining anode, to unidirectional beams. The tube having these design features including the beam forming plates is characterized by an unusually high transconductance and its anode characteristic is such that the tube passes a large current under the static condition with the control electrode at or near zero potential or preferably slightly negative, while the tube cuts off substantially with only a, moderate negative voltage on the control electrode.

In the operation of radio transmitters it is often desirable that certain circuits of the transmitter be cut off during prolonged non-operating periods of the transmitter keying circuit. It is a further object of my present invention to provide improved means, cooperating with the keying means, for such oonti'ol of certain circuits of the transmitter. In accordance with the invention,

for this purpose a relay means to control the above-mentioned certain circuits is provided which is arranged to be operated positively and efiiciently by the relatively high current supplied from a second tube of the above-mentioned beam type the control electrode bias voltage 01' which is controlled, simultaneously with that of the beam type keying tube, by the keying device.

The novel features which are considered to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing the single figure of which is a diagrammatic representation of a radio transmitter embodying my invention.

In the single figure of the drawing the numeral I designates an electron discharge device or tube which may be an intermediate amplifier tube of a radio transmitter the other several stages of which, of any usual or preferred form, preceding and following the amplifier I, are omitted for clearness. One or more tubes may be connected for operation in parallel with tube I. The numeral 2 designates an electron discharge device or tube which is of the above-mentioned beam type and which is arranged to function as a key-'- ing' tube in series with the amplifier I. The cathode 3 of amplifier I is connected to the anode 4 of keying tube 2, and the anode 5 of amplifier I and the cathode 6 of keying tube 2 are connected respectively to opposite terminals of an anode voltage source (not shown), for example across a potentiometer I connected to the latter source The discharge device 2 comprises in addition to anode 4 and cathode 6 a screen grid or electrode Ia, and a control grid or electrode 8. The device-2- is of the type wherein the electrons proceeding from cathode to anode through the control electrode and screen electrode are conmoving between cathode and strained to form unidirectional and undeviating beams by means comprising beam-forming plates 8a connected to and at the potential of the cathode and mounted in the electron path, between the control and screen electrodes and the anode. The screen grid Ia of tube 2 is connected to a suitable point of potentiometer I.

To impress upon the control electrode, 8, of keying tube 2 of normal voltage negative with respect to cathode 6 and corresponding approximately to the cutoff point of this tube, the control electrode 8 and the cathode 8 are connected to a suitable voltage source (not shown), preferably respectively to negative and positive connection points 9 and III of a potentiometer II,

or portion thereof, connected to the latter voltage source. Preferably the control electrode circuit thus including cathode 6, control electrode 8, and potentiometer I I is completed through a resistance means I2, which may be a voltmeter, connecting cathode 6 to the positive connection point III of potentiometer II.

To change the bias voltage of control electrode 8 in the positive direction to a value at which the keying tube 2 becomes conducting to a desired degree, a means is provided, preferably located at a control station or control point I3 remote from the transmitter apparatus including tubes I and 2 and the above described negative biasing means for control electrode 8, to oppose or neutralize a portion of the voltage due to the latter negative biasing means.

This remote control means may include an auxiliary bias voltage source (not shown) which may be connected across a potentiometer I4, and a keying device, designated in general by the numeral I5, which may be any usual or preferred device for keying at any desired speed.

A two-conductor line I6 comprising the conductors I1 and I8 extends between the remote control apparatus and the above described means,

I comprising potentiometer II and resistance I2,

for impressing a normal negative bias voltage upon control electrode 8 corresponding to the cutofi point of keying tube 2. The two-conductor line I6 is arranged to connect in opposition the normal bias voltage source including potentiometer II, and the auxiliary bias voltage source including potentiometer I4. One of the conductors as IT, is arranged for example to connect together terminals of like polarity of the two potentiometers, as positive terminal I0 of potentiometer II and positive terminal I9 of potentiometer I4. The other termin is of like polarity, i. e., 9 of potentiometer I I and o of potentiometer I4, are adapted to be connected together through the keying device I5, the other conductor I8 of the two-conductor line, and the space path betweer; cathode B and control electrode 8 of keying ube The auxiliary bias voltage source including potentiometer I4 is illustrated herein as grounded at the positive extremity thereof. It is to be understood, however, that the auxiliary voltage source may be grounded if desired at either the circuits (not shown), a time delay relay 2| of any usual or desired type is provided having contacts 22 adapted to be connected to the auxiliary control circuits, and an actuating winding 23 arranged to be energized by current from an electron discharge device or tube 24 connected essentially in parallel with the keying tube 2. These auxiliary circuits, not shown, may include,

, for example, a time delay circuit for cutting off an oscillator after a five second interval during receiving periods of the transmitter, a time delay circuit for placing the transmitter, after a five minute interval, in the standby condition, and a time delay circuit for shutting down the equipment completely after a fifteen minute interval. The relay 2| is so arranged that the contacts 22 open quickly when winding 23 becomes energized and close with a predetermined time delay when winding 23 becomes deenergized.

In accordance with the present invention the relay control tube 24, like the keying tube 2, is of the hereinabove described beam 'type. The cathode 25 of control tube 24 is connected in parallel with the cathode 6 of keying tube 2, the

anode 26 of tube 24 is connected through the actuating winding 23 of time delay relay 2| to a suitable point of potentiometer 1, and the control electrode 21 is connected in parallel with the control electrode 8 of tube 2.

In operation of the system illustrated in the figure, let it be assumed first that the keying device i is being maintained for a period of substantial length in the open illustrated position,'

during a reception period of the transmitter for example. Then during this period a biasing voltage is being impressed from potentiometer ll through the resistance |2 of the voltmeter upon control electrode 8 of keying tube 2. This voltage is negative by a predetermined amount, preferably 35 volts or thereabout relative to the cathode 6, and the screen grid Id of tube 2 is at a positive potential of about 250 volts relative to cathode 6. This relatively small negative bias in the tube 2, which tube in, accordance with the present invention is of the beam type as hereinabove described, is yet sufiicient substan-- tially to block the tube. The anode circuit of the latter tube therefore presents a very high impedance, preventing flow of anode current in the amplifier tube I which is in series therewith.

The flow of current in the anode circuit of relay control tube 24 and in the actuating winding 23 of relay 2| is also blocked during this prolonged period since the control electrode circuits of tubes 24 and 2 are in parallel. The relatively low 35 volt negative bias of control electrode 21 of tube 24 relative to cathode 25 thus causes tube 24 to present a high impedance to the flow of energizing current in actuating winding 23. The contacts 22 of relay 2| are therefore being maintained in their illustrated closed position and the auxiliary time delay circuits (not shown) hereinabove mentioned, connected to the contacts of relay 2| are maintained in energized condition.

The transmitter during the assumed prolonged period that the keying device l5 remains in the open position is thus maintained in partially or completely non-operating condition, the ampliher I being in inoperative or non-keying condition and the auxiliary contacts 22 of relay 2| being closed for the purpose of energizing the above mentioned auxiliary circuits of the transmitter to cut off portions of the apparatus or to shut down the transmitter altogether, depending upon the of keying tube 2. Since the tube 2 is of the above-described beam type the decrease in the bias voltage from its relatively small normal cutoff value to a different but still negative voltage, for example to five volts negative bias voltage, causes the impedance presented by the anode circuit of tube 2 to decrease to a low value, the

voltage drop across this tube at milliamperes anode current becoming, for example, only of the order of 30 volts. Since the impedance presented,v by keying tube 2 in the series circuit including amplifier tube I thus becomes small, the anode current of the latter tube assumes its normal value and a keying pulse is transmitted therefrom.

Simultaneously with the change from the 35 volt negative bias to the 5 volt negative bias impressed upon the control electrode 8 of keying tube 2, a like change in bias voltage impressed upon control electrode 21 of relay control tube 24 occurs. The impedance presented by the latter beam type tube to the energizing current for actuating winding 23 of time delay relay 2| also becomes small, winding 23 becomes energized and immediately opens the contacts 22 of this relay. All circuits of the transmitter are now in operative condition. v During a continued keying period of the amplifier tube by the keying device IS the contacts 22 of time delay relay 2| remain continuously in the open position and the auxiliary circuits (not shown) controlled by this relay are not energized. However, when keying of the transmitter by keying device I5 ceases, the contacts 22 of relay 2| close after a short interval. The cycle of operation as above described may be repeated indefinitely.

It will be seen that in accordance with my present invention I have provided a transmitter keying system in which by the incorporation therein of a tube of the above-described beam type as a keying tube and of a second like beam type tube in parallel therewith as a time delay control tube, efficient control of the transmitter durnecting line l6 carries no current or substantially none, the conductors thereof are small. Since the keying device at the remote station operates to control the bias voltage of the keying and control tubes 2 and 24 directly by voltage varlation in the connecting line I6 and without the use of relays between the keying device and the transmitter proper, the required high keying speeds, up to the speeds required for facsimile operation, are easily attained, relays for this purpose requiring relatively heavy operating current in the connecting line and not being capable of suiiiciently rapid action for speeds of the required order of 1000 words per minute. Since the keying tube 2 and the time delay relay control tube 24 are of the above-described beam type, the required'relatively heavy keying current of the order of 100 millia'mperes in the amplifier tube l is obtained with a voltage drop of the order of 30 volts only' in the keying tube, and likewise the required relatively heavy energizing current for time delay relay 2| is obtained with a correspondingly low voltage drop in the control tube. v

My'invention has been described herein in a particular embodiment for purposes of illustration. It is to be understood, however, that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope of my invention.

' What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a transmitter comprising an electron discharge device having an anode-cathode circuit, an electron discharge device having a cathode, an anode, a control electrode and a screen electrode and being of the type wherein the electrons proceeding from cathode to anode through said electrodes are constrained to form unidirectional beams by means comprising electronbeam-forming plates connected to and at the potential of said cathode and mounted between said electrodes and said anode, means to connect the anode-cathode circuits of said discharge devices in series, and means to change the bias voltage impressed upon said control electrode of said second-named device relative to its cathode from a negative value corresponding substantially to the cutoff point of said second-named device to a-small value, thereby to reduce substantially the impedance presented by said second-named device to current'flow in said anodecathode circuits.

2. In a transmitter comprising an electron discharge device having an anode-cathode circuit, an electron discharge device having a cathode, an anode, a control electrode and a screen electrode and being of the type wherein the electrons proceeding from cathode to anode through said electrodes are constrained to form unidirectional beams by means comprising electron-beamforming plates connected to and at the potentialof said cathode and mounted between said electrodes and said anode, means to connect the anode-cathode circuit of said second-named device inseries with said first-named circuit, means to impress upon said control electrode of said second-named device a bias voltage sufliciently negative relative to its cathode to cause said second-named device to present a high impedance to curent flow in said anode-cathode'c'ircuits', and means remote from .said electron discharge devices to change said bias voltage to a value such that a low impedance is presented to said current flow. i

3. In a transmitter comprising an electron discharge device having an anode-cathode circuit, an lectron discharge device having a cathode, an anode, a control electrode and a screen electrode and being of the type wherein the electron proceeding from cathode to anode are constrained to form unidirectional beams by means comprising electron-beam-forming plates connected to and at the potential of the cathode and mounted between said electrodes and said anode-cathode circuit of said second-named device in series with said first-named circuit, means to impress upon said control electrode of said second-named device a bias voltage sufliciently negative relative to its cathode to cause said second-named device to present a high impedance to current flow in said anode-cathode circuits, and means remote from said discharge devices to impress upon said control electrode a voltage opposing said bias voltage to reduce the voltage of said control electrode relative to the cathode of said second-named device to a low negative value. v

4. In a transmitter comprising an electron discharge device adapted to transmit current pulses, means to key said device comprising an electron discharge device having a cathode, an anode, a control electrode and a screen electrode and being of the type wherein the electrons proceeding from cathode to anode through said electrodes are constrained to form unidirectional beams by means comprising electron-beam-forming plates connected to and at the potential of said cathode and mounted between said electrodes and said anode, means to connect the anode-cathode circuit of said second-named device in series wtih the anode-cathode circuit of said first-named device, means to cause said second-named device to present a high impedance to current flow in the anode-cathode circuit of said first-named device, and means remote from said devices and including a keying device to reduce said impedance to a low value whereby a current pulse is transmitted from said first-named device.

5. In a transmitter comprising an electron discharge device adapted to transmit current pulses, means to key said device comprising an electron discharge device having a cathode, an anode, a control electrode and a screen electrode and being of the type whereinthe cathode to anode through said electrodes are constrainedto form unidirectional beams by means comprising electron-beam-forming plates connected to and at the potential of said cathode and mounted between said electrodes and said anode,

means to connect the anode-cathode circuit ofv said second-named device in series'with the anmeans to impress upon said control electrode of said second-named device a voltage sufliciently negative relative to the cathode thereof to cause said second-named devic to present a high impedance to current flow in the anode-cathode circuit of said first-named device, and means remote from said electron discharge devices and including a keying device to reduce said voltage to a small value such that a low impedance is presented by said second-named device to said current flow whereby a current pulse is transmitted from said first-named device.

6. In a transmitter, an electron discharge device adapted to transmit current pulses, a time delay device having an energizing winding, and means to control simultaneously the operation of said devices, said means comprising a beam type electron discharge device having its anode-cathode circuit connect d in series with the anodecathode circuit of said first-named device, a, second beam type electron discharg device having its control electrode-cathode circuit connected in parallel with-the control electrode-cathode cirelectrons proceeding from means to key said electron discharge device and to control simultaneously with said keying the operation of said time delay device, said means comprising a beam type electron discharge device having the anode-cathode circuit thereof connected in series with the anode-cathode circuit of said first-named-de'vi'ce, a, second beam type electron discharge device having the control electrode-cathode circuit thereof connected in parallel with the control electrode cathode circuit of said first-named beam type device and having an anode-cathode circuit including said winding, means to impress upon the control electrodes of said beam type devices a, bias voltage substantially negative with respect to the cathodes thereof, and means including a keying device remote from said electron discharge devices to reduce said bias voltage to a small negative value.

8. In a transmitter comprising an electron discharge device adapted to transmit current pulses of the order of 80 to 100 milliamperes at a speed corresponding at least to 1000 words per minute, means to key said device comprising an electron discharge device having a cathode, an anode, a. control electrode and a screen electrode and being of the type wherein the electrons proceeding from cathode to anode are constrained to form unidirectional beams by means comprising electronbeam-forming plates connected to and at the potential of said cathode and mounted between said electrodes and said anode, means to connect the anode-cathode circuit of said second-named device in series with the anode-cathode circuit of said first-named device, means to impress upon said control electrode a bias voltage 01 the order of '35 volts negative relative to said cathode thereby to cause said second-named device to asl sume substantially the cutoff. condition,. and

means remote from said electron discharge devices and including a keying device to reduce said bias voltage to a small value negative relative to said cathode thereby to cause the voltage drop across said cathode and anode in said secondnamed device to be reduced to a value or the order of 30 volts. Y

PAUL D. ANDREWS. 

